Started last Wednesday, Went to ride and on the 4th lap I noticed that it (2007 YZ450f) wasn't decelerating all the way to idle at first. after two more laps of it getting progressively worse, I pulled off. I sat the bike on the stand and would rev the bike. It would rev clean, the throttle would snap back shut when let go but the rpm would only come down to maybe 2500 rpm..... hold for a second or two and then come all the way down to idle. Over the next few days I: 1. Changed the gas in case of bad gas 2. Took the carb apart to find nothing wrong cleaned the carb, jets, accellerator pump, etc 3. Checked wiring and re-lubed with dielectric grease. 4. with running, sprayed the fore and aft carb boots with chemtool and did not change the idle (no air leak). Still does the same thing, not as bad and not consistent. Sometimes it will decelerate all the way to idle and then sometimes it still hangs up. I checked the slide and it is shutting properly without any hesitation. Also, when trying to adjust the idle screw, I can adjust almost 2 full turns without a change in idle speed and then all of a sudden it falls off and dies. I tried to make sure that the fuel screw was set correctly but without it idling properly I can't really adjust it. I set it at 2.25 turns out which is where I had it set prior to these problems. Nothing was different from the time before riding when it ran fine. Came home, washed off, started back up after washing to let it heat up and then put her in the garage. three days later is when all of this started happening. Any ideas as to what could be occurring?